1. Field of the Invention
The present invention relates to a relative-displacement detecting unit and a relative-displacement detecting device; and more particularly to a technique to achieve the size reduction and high accuracy detection of a unit for outputting its displacement relative to a scale in the form of an electrical signal.
2. Description of the Related Art
In related art, a transducer or an encoder for detecting relative displacement is known. In a capacitance-type encoder, a transmission electrode and a reception electrode are provided on a grid (unit), and a signal electrode is provided on a scale opposing this unit. The transmission electrode and the reception electrode on the unit are capacity-coupled with the signal electrode on the scale. A drive signal is supplied to the transmission electrode, and a detected signal occurring in the reception electrode in correspondence with the relative position of the unit and the scale is processed by a processing circuit. Thus, it is possible to detect the movement or the position of the unit with respect to the scale. In an induction-type encoder, the relative position is detected on the basis of the electromagnetic interaction (electromagnetic induction) between the unit and the scale. Namely, a transmission coil (excitation coil) and a detection coil are disposed on the unit, and a scale coil is formed on the scale. As current is fed to the excitation coil on the unit, a magnetic flux occurs, and an induced current is generated in the scale coil on the scale by electromagnetic induction. A magnetic flux is generated by the induced current generated in the scale coil, and an induced current (induced voltage) is generated in the detection coil on the unit by the magnetic flux. Since the induced voltage varies in correspondence with the relative position of the excitation coil and the scale coil, the relative position of the unit and the scale can be detected by detecting the induced voltage generated in the detection coil. In the encoder as mentioned above, much effort has been made to reduce the size of both the unit and scale, with an intention of increasing a detection accuracy and reducing the size of the unit and scale.
Even if the unit size is reduced, stray inductance and capacitance (stray LC) are present among the wires connecting the unit to its peripheral electric circuits and will degrade the encoder performance unless the peripheral electric circuits are integrated together with the unit.
Accordingly, an object of the present invention is to reduce the stray LC by integrating the encoder unit and its peripheral electric circuits on a substrate.
The above-mentioned object can be achieved by a relative-displacement detecting unit, according to the present invention, disposed facing a scale, for detecting its displacement relative to the scale and outputting a detected relative-displacement in the form of an electrical signal. The relative-displacement detecting unit includes a read head and a processing circuit. The read head detects a displacement of the relative-displacement detecting unit relative to the scale. The processing circuit drives the read head, processes signal output from the read head, and outputs the processed signal to exterior. The read head and the processing circuit are integrally formed on a semiconductor substrate.
Since the read head and the processing circuit are both integrally formed on a semiconductor substrate, the stray LC caused by wiring is suppressed and hence size reduction and high accuracy detection are realized. Here, xe2x80x9cto integrally formxe2x80x9d means not only to form those circuits on one and the same surface of the substrate, but also to form those circuits on different layers of the substrate.
The relative-displacement detecting unit may further comprise a magnetic shielding layer provided between the read head and the processing circuit. In the invention, the read head and the processing circuit are formed close to each other. A magnetic field developed from the read head directly affects the processing circuit (This phenomenon is called cross talk.). Provision of the magnetic shielding layer between the read head and the processing circuit prevents the cross talk. This results in increase of detection sensitivity. The magnetic shielding layer is made of high magnetic permeability material, e.g., ferrite, or may be a metal layer.
In the above-mentioned relative-displacement detecting unit, the processing circuit is preferably formed by a patterning process, and the read head is preferably formed by a resin buildup process. The relative-displacement detecting unit of the invention is integrally formed on a semiconductor substrate. In this case, the same forming process is not always used for forming the processing circuit and the read head. Rather, an active element portion (processing circuit portion) and a passive element portion (read head portion) may be formed by different forming processes.
Since the relative-displacement detecting unit is integrally formed on the semiconductor substrate, various mounting methods may selectively be used when the unit is mounted on a board. The relative-displacement detecting unit is mounted on a board by wire bonding, thereby forming a relative-displacement detecting device. The relative-displacement detecting unit may be mounted on a board by use of flip chips. Further, the relative-displacement detecting unit may be incorporated into a package mounted on a board.